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Date:   Mon, 21 Nov 2022 15:13:21 +0100
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Subject: Re: [PATCH 2/3] acpi/processor: sanitize _PDC buffer bits when
 running as Xen dom0
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From:   Jan Beulich <jbeulich@suse.com>
To:     Roger Pau Monne <roger.pau@citrix.com>
Cc:     xen-devel@lists.xenproject.org, jgross@suse.com,
        stable@vger.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20221121102113.41893-1-roger.pau@citrix.com>
 <20221121102113.41893-3-roger.pau@citrix.com>
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On 21.11.2022 15:10, Jan Beulich wrote:
> On 21.11.2022 11:21, Roger Pau Monne wrote:
>> --- a/drivers/acpi/processor_pdc.c
>> +++ b/drivers/acpi/processor_pdc.c
>> @@ -137,6 +137,14 @@ acpi_processor_eval_pdc(acpi_handle handle, struct acpi_object_list *pdc_in)
>>  		buffer[2] &= ~(ACPI_PDC_C_C2C3_FFH | ACPI_PDC_C_C1_FFH);
>>  
>>  	}
>> +	if (xen_initial_domain())
>> +		/*
>> +		 * When Linux is running as Xen dom0 it's the hypervisor the
>> +		 * entity in charge of the processor power management, and so
>> +		 * Xen needs to check the OS capabilities reported in the _PDC
>> +		 * buffer matches what the hypervisor driver supports.
>> +		 */
>> +		xen_sanitize_pdc((uint32_t *)pdc_in->pointer->buffer.pointer);
>>  	status = acpi_evaluate_object(handle, "_PDC", pdc_in, NULL);
> 
> Again looking at our old XenoLinux forward port we had this inside the
> earlier if(), as an _alternative_ to the &= (I don't think it's valid
> to apply both the kernel's and Xen's adjustments). That would also let
> you use "buffer" rather than re-calculating it via yet another (risky
> from an abstract pov) cast.

Oh, I notice this can end up being misleading: Besides having it in the
earlier if() we had also #ifdef-ed out that if() itself (keeping just
the body). The equivalent of this here might then be

	if (boot_option_idle_override == IDLE_NOMWAIT || xen_initial_domain()) {

Jan